Multiple pressure fluid system

ABSTRACT

A fluid system having a variable displacement fluid direct fluid in a closed loop circuit to a fluid cylinder having a piston and a pair of connecting rods extending from opposite sides of the piston externally of the fluid cylinder. A main directional control valve disposed in the closed circuit between the inlet and outlet of the fluid pump is adapted to selectively direct fluid to one side of the piston within the fluid cylinder, while exhausting fluid from the other side of the piston, to selectively move the piston within the fluid cylinder. The rate of movement of the piston in either direction of movement is controlled by the amount of fluid displaced by the fluid pump. A second directional control valve is adapted to fluid FLUID from a second source of fluid to a pressure responsive displacement control mechanism to selectively vary the displacement of the fluid pump between a maximum and a minimum value. The rate of fluid flow to the pressure responsive displacement control mechanism is selectively varied to control the rate of displacement of the fluid pump and to thereby selectively control the rate of movement of the cylinder piston. A remotely controlled pilot operated pressure relief valve, having an inlet connection in fluid communication with the outlet conduit of the fluid pump upstream from the main directional control valve and an outlet connection in fluid communication with the inlet conduit of the fluid pump between the fluid pump and the main directional control valve, is operable to reduce the normal operating pressure in the outlet conduit, and thus the operating pressure of the fluid in the main fluid cylinder, to a lower predetermined value when the pressure responsive displacement control mechanism is actuated to vary the displacement of the fluid pump toward a minimum value.



1. A multiple pressure fluid system comprising: a fluid pump having a high pressure fluid outlet and a low pressure fluid inlet; a fluid motor having an output means responsive to fluid pressure for generating a movable mechanical output; first motor port means adapted to communicate fluid pressure to said output means to move said mechanical output in one direction, and second motor port means adapted to communicate fluid pressure to said output means to move said mechanical output in an opposite direction; a first conduit means connecting said pump high pressure outlet to one of said motor port means for communicating fluid pressure thereto; a second conduit means connecting said pump low pressure inlet to the other of said motor port means for exhausting fluid pressure therefrom, such that said pump and motor are connected in a closed loop fashion; controlleD means connected to said first conduit means and operable upon actuation while said fluid pressure is being delivered from said pump to said motor for reducing the pressure in said first conduit means to a lower predetermined value; means for actuating said controlled means in response to said fluid motor mechanical output after same has moved a predetermined distance in a selected direction, said pump continuing to deliver fluid pressure at said predetermined value after said controlled means is actuated; and a valve means, said first and second conduit means comprising a first fluid line and a second fluid line respectively communicating said pump high pressure outlet and low pressure inlet to said valve means, and a third fluid line and a fourth fluid line respectively communicating said first and second motor port means to said valve means, said valve means selectively connecting said first and second fluid lines to said third and fourth fluid lines such that the high pressure fluid in said first fluid line is directed selectively to one of said third or fourth fluid lines to move said output member in opposite directions, while fluid in the other said third or fourth fluid line is exhausted through said second fluid line, said controlled means comprising a pressure relief valve having its inlet connected to said first fluid line and its outlet connected to said second fluid line; and pilot valve means selectively operable to control the pressure at which said relief valve opens, whereby the pressure in said first fluid line carrying said high pressure fluid may be selectively reduced to said lower predetermined value after said mechanical output is moved a predetermined distance.
 1. A multiple pressure fluid system comprising: a fluid pump having a high pressure fluid outlet and a low pressure fluid inlet; a fluid motor having an output means responsive to fluid pressure for generating a movable mechanical output; first motor port means adapted to communicate fluid pressure to said output means to move said mechanical output in one direction, and second motor port means adapted to communicate fluid pressure to said output means to move said mechanical output in an opposite direction; a first conduit means connecting said pump high pressure outlet to one of said motor port means for communicating fluid pressure thereto; a second conduit means connecting said pump low pressure inlet to the other of said motor port means for exhausting fluid pressure therefrom, such that said pump and motor are connected in a closed loop fashion; controlleD means connected to said first conduit means and operable upon actuation while said fluid pressure is being delivered from said pump to said motor for reducing the pressure in said first conduit means to a lower predetermined value; means for actuating said controlled means in response to said fluid motor mechanical output after same has moved a predetermined distance in a selected direction, said pump continuing to deliver fluid pressure at said predetermined value after said controlled means is actuated; and a valve means, said first and second conduit means comprising a first fluid line and a second fluid line respectively communicating said pump high pressure outlet and low pressure inlet to said valve means, and a third fluid line and a fourth fluid line respectively communicating said first and second motor port means to said valve means, said valve means selectively connecting said first and second fluid lines to said third and fourth fluid lines such that the high pressure fluid in said first fluid line is directed selectively to one of said third or fourth fluid lines to move said output member in opposite directions, while fluid in the other said third or fourth fluid line is exhausted through said second fluid line, said controlled means comprising a pressure relief valve having its inlet connected to said first fluid line and its outlet connected to said second fluid line; and pilot valve means selectively operable to control the pressure at which said relief valve opens, whereby the pressure in said first fluid line carrying said high pressure fluid may be selectively reduced to said lower predetermined value after said mechanical output is moved a predetermined distance.
 2. A multiple pressure fluid system comprising: a fluid pump having a high pressure fluid outlet and a low pressure fluid inlet; a fluid motor having an output means responsive to fluid pressure for generating a movable mechanical output; first motor port means adapted to communicate fluid pressure to said output means to move said mechanical output in one direction, and second motor port means adapted to communicate fluid pressure to said output means to move said mechanical output in an opposite direction; a first conduit means connecting said pump high pressure outlet to one of said motor port means for communicating fluid pressure thereto; a second conduit means connecting said pump low pressure inlet to the other of said motor port means for exhausting fluid pressure therefrom, such that said pump and motor are connected in a closed loop fashion; a valve means, said first and second conduit means comprising a first fluid line and a second fluid line respectively communicating said pump high pressure outlet and low pressure inlet to said valve means, and a third fluid line and a fourth fluid line respectively communicating said first and second motor port means to said valve means, said valve means selectively connecting said first and second fluid lines to said third and fourth fluid lines such that the high pressure fluid in said first fluid line is directed selectively to one of said third or fourth fluid lines to move said output member in opposite directions, while fluid in the other said third or fourth fluid line is exhausted through said second fluid line; a first pressure relief valve having its inlet connected to said third fluid line and its outlet connected to said fourth fluid line; a second pressure relief valve having its inlet connected to said fourth fluid and its outlet connected to said third fluid line; and pilot valve means selectively operable in response to a predetermined movement of said fluid motor output to control the pressure at which said first and second relief valves open, whereby the pressure in whichever of said fluid lines carrying said high pressure fluid may be selectively reduced to a lower predetermined value.
 3. A multiple pressure fluid system comprising: a variable displacement Fluid pump having high pressure fluid outlet and a low pressure fluid inlet; a fluid motor having an output member movable in response to fluid pressure; first motor port means adapted to communicate fluid pressure to said output member to move said output member in one direction, and second motor port means adapted to communicate fluid pressure to said output member to move said output member in an opposite direction; a first conduit means connecting said pump high pressure outlet to one of said motor port means; a second conduit means connecting said pump low pressure inlet to the other of said motor port means; remotely controlled means connected to said first conduit means for selectively reducing the pressure in said first conduit means to a lower predetermined value after said fluid motor output member moves a predetermined distance in a selected direction; pressure responsive means for varying the fluid displacement of said variable displacement pump; a second source of fluid pressure; first means for communicating said second source of fluid pressure to said pressure responsive displacement varying means at a selected rate to control the rate of change in the increase in the displacement of said fluid pump to accelerate said motor output member; second means alternately operable from said first means, said second means communicating said second source of fluid pressure to said pressure responsive displacement varying means at a second selected rate to control the rate of change in the decrease in the displacement of said fluid pump to decelerate said output member; and means actuating said remotely controlled means simultaneously with actuation of said second means whereby the pressure of the fluid moving said output member decreases to said lower predetermined value as said output member decelerates.
 4. The multiple pressure fluid system defined in claim 3 wherein said fluid motor means comprises a main fluid cylinder having a piston reciprocably mounted therein and movable in response to the fluid pressure acting on the opposite sides of said piston, the effective pressure responsive areas on the opposite sides of said piston being equal; said fluid system further comprising valve means selectively connecting the inlet and outlet of said fluid pump to the opposite sides of said piston to direct fluid to said piston and exhaust fluid from the other side of said piston to move said piston.
 5. The multiple pressure fluid system defined in claim 3 wherein said remotely controlled means comprises a remote control relief valve having an inlet connected to said first conduit means and an outlet connected to said second conduit means whereby said relief valve is operable to direct fluid from said first conduit means to said second conduit means.
 6. The multiple pressure fluid system defined in claim 3 further comprising a directional control valve connected to said first and second conduit means for selectively connecting said first and second conduit means to said fluid motor first and second port means, said remotely controlled means comprising a remote control relief valve having its inlet connected to said first conduit means and its outlet connected to said second conduit means.
 7. The multiple pressure fluid system defined in claim 3, further comprising a valve means, said first and second conduit means comprising a first fluid line and a second fluid line respectively communicating said pump high pressure outlet and low pressure inlet to said valve means and a third fluid line and a fourth fluid line respectively communicating said first and second motor port means to said valve means, said valve means selectively connecting said first and second fluid lines to said third and fourth fluid lines such that the high pressure fluid in said first fluid line is directed selectively to one of said third or fourth fluid lines to move said output member in opposite directions, while fluid in the other of saId third or fourth line is exhausted through said second fluid line, said remote controlled means comprising a first remote control relief valve having its inlet connected to said third fluid line and its outlet connected to said fourth fluid line, and a second remote control relief valve having its inlet connected to said fourth fluid line and its outlet connected to said third fluid line, whereby the pressure in whichever of said fluid lines carrying said high pressure fluid may be selectively reduced to a lower predetermined value after said movable output member is moved a predetermined distance. 